Field of the Invention
The present invention relates to a positive electrode active material used in non-aqueous electrolyte secondary batteries, such as a lithium ion secondary battery and a method of producing the same.
Description of the Related Art
In recent years, mobile devices such as VTR, mobile phone and note PC have been spreading and miniturization of those have been in progress. For the power source of those mobile devices, a non-aqueous electrolyte secondary batteries, such as a lithium ion secondary battery has been employed. Furthermore, the non-aqueous electrolyte secondary battery has attracted a great deal of attention as a power battery for electric vehicles and the like so as to cope with recent environmental problems.
There has widely been employed, as a positive electrode active material for a lithium secondary battery, lithium cobalt oxide that can constitute a 4V class secondary battery.
Cobalt, that is a constituent component of a raw material for lithium cobalt oxide, is a scarce resource and the regions of cobalt deposits are also unevenly distributed, which leads to high costs and causes anxiety about supply of the raw material.
In response to these circumstances, lithium transition metal composite oxides which have a stacked-layer structure such as nickel-cobalt-lithium manganate in which a part of Co in lithium cobalt oxide is substituted with other metals such as Ni and Mn, have been developed.
There have been technologies for incorporating a specific polyvalent metal on the surface of particles of a lithium transition metal composite oxide for various purposes. The type of polyvalent metal and the way to contain the polyvalent metal differ variously according to purposes.
JP 2002-75367A describes lithium composite oxide powder which is subjected to a coating treatment to form a surface layer containing Li and at least one element selected from the group consisting of Mo and W, in order to achieve both high initial charge-discharge capacity and heat stability. More specifically, JP 2002-75367A describes a method in which a lithium nickelate-based composite oxide with part of Ni substituted with Co and Al, and Li2MoO4 or Li2WO4 are mixed and the mixture is subjected to a hear treatment at 714° C. or 752° C.
JP 2000-315502A describes a positive electrode active material in which, in order to improve safety at occurrence of internal short circuit, at least one element selected from V, Nb, W, Mo, and the like is contained in a composite oxide which contains lithium and nickel as the main components. More specifically, JP 2002-75367A describes a method in which a lithium nickelate-based composite oxide with part of Ni substituted with Co and Al, and Nb2O5 or V2O5 or the like are suspended in a lithium nitride solution, then subjected to wet crushing and spray drying to give granulated particles, which is then subjected to a hear treatment at 800° C.
In addition to those, there has been a technique of incorporating boron into the surface of lithium transition metal composite oxide.
JP 2009-146739A discloses a technology in which on the surfaces of lithium transition metal composite oxide particles which contains nickel or cobalt as an essential component, a boric acid compound such as ammonium borate, lithium borate, or the like, is deposited, and is subjected to heat-treatment under an oxidation atmosphere to obtain high capacity of a secondary battery and to improve discharging efficiency and charging efficiency of of the secondary battery. In JP 2009-146739, only lithium nickelate in which a part of nickel is substituted with cobalt and aluminum is disclosed as lithium transition metal composite oxide.